In an effort to reduce back pain through early intervention techniques, some investigators have focused upon nerves contained within the vertebral bodies.
For example, PCT Patent Publication No. WO 01/0157655 (“Heggeness”) discloses ablating nerves contained within the vertebral body by first boring into the vertebral body with a nerve ablation device, placing the tip of the device in close proximity to the nerve, and then ablating the nerves with the tip. Heggeness discloses numerous devices, such as electricity transmitting probes, as candidate nerve ablation devices. In describing how to use such as probe, Heggeness discloses “raising the temperature of tip 24 such that the intraosseous nerve is ablated by the heat generated by electrical current passing through tip.” See Heggeness at page 8, line 28. The probe disclosed by Heggeness appears to be a solid metal rod functioning as the active electrode of a monopolar Rf device.
U.S. Pat. No. 6,478,793 (“Cosman”) discloses ablative treatment of metastatic bone tumors, including those within the spine. Pain relief is reportedly achieved by penetrating the bone wall with a suitable probe, and applying heat through the probe to ablate either the bone tumor or the tissue near the bone tumor. Cosman teaches the use of both monopolar and bipolar probes in this application. See Cosman at col. 5, line 44. Cosman also teaches that the treatment may also be used to ablate the nerves and nerve ramifications in and/or around the bone to desensitize them against further tumor encroachment. See Cosman at col. 8, line 50–65, and col. 9, lines 9–17.
The only probes specifically disclosed by Cosman appear to be monopolar. However, monopolar approaches require the use of a grounding pad beneath the patient and allows energy to flow from the probe and to dissipate in the surrounding tissue. Because the path by which the energy flows from a monopolar probe to its corresponding pad is uncontrolled, the energy may undesirably flow through sensitive tissue, such as the spinal cord. Since this method may cause undesired local muscle or nerve stimulation, it may be difficult or dangerous to operate in sensitive areas of the human body.
Cosman teaches that the electrode may be rigid and robust and capable of piercing bone. Cosman teaches that the electrode may comprise a metal tubular shaft (with appropriate wall thickness to prevent buckling or bending during penetration of hard bone) with a rugged pointed tip. See Cosman at col. 6, lines 34–46. Beyond teaching the use of a generic bipolar probe, Cosman does not disclose any particular bipolar electrode configuration.
U.S. Pat. No. 6,168,593 (“Sharkey”) discloses thermal probes in which the electrodes are disposed at an angle to the longitudinal axis of the probe. In one embodiment, an electrode is located in a laterally—disposed window of a tubular, electrically insulating shaft. See FIG. 1A. According to Sharkey, this electrode can ablate tissue at an angle to the principal axis of the probe.
Although the probe disclosed in FIG. 1A of Sharkey appears to be monopolar, Sharkey also teaches that “bipolar delivery can be implemented using the techniques of the current invention by providing at least two distinct elements on the tip, each connected to outgoing and return electrical paths from the RF power supply.
Sharkey does not disclose a return and an active electrode located within the same window. Sharkey does not disclose a window in a conductive shaft. Sharkey does not disclose a probe having a tip adapted to penetrate bone.
U.S. Pat. No. 5,944,715 (“Goble”) discloses electrosurgical instruments wherein active electrodes 14 are housed within a window of an insulator. See FIGS. 1 and 4.
Like Sharkey, Goble does not disclose a return and an active electrode located within the same window, nor a window in a conductive shaft, nor a probe having a tip adapted to penetrate bone.